System of control.



R. E. HELLMUND.

SYSTEM OF CONTROL.

APPLICATION FILED SEPT-8.1914.

1,300,387, Patented Apr. 15,1919.

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SYSTEM OF CONTROL. APPLICATION FILED SEPT. 8 1914.

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- 1. c wrmssszs: 26mm r INVENTOR BY 3 Z ATTORNEY UNITED STATES PATENT OFFICE.

BUDOLF E. HELLMUND, OF PITTSBURGH, PEN N SYLVANIA,ASSIGNOR TO WESTINGHOUSE ELECTRIC AN D UFAOTURING COMPANY, A CORPORATION OF PENNSYLVANIL SYSTEM or common.

Specification of Letters Patent.

Patented Apr. 15, 1919.

Application filed September 8, 1914, Serial No. 860,611. 1

To all whom it may concern.

Be it known that I, RUDoLr E. HELL- MUND, a subject of the Emperor of. Germany, and a resident of Pittsburgh, in the county of Allegheny and State of Pennsylvania, have invented. a new and useful Improvement in Systems of Control, of which the following is a specification.

My invention relates to alternating-current motors of the series commutating type, and it has for its object to provide means whereby the speed of a motor of the character specified may be controlled in a simple and effective manner and, at the same time, the commutating reactance voltage may be substantially neutralized at all speeds, and commutator sparking eliminated.

In the operation of alternating-current motors of the series commutating type, it is common to control the speed of rotation of the armature by supplying the armature winding with current from two sources, namely, by induction from a cross field winding" and by direct flow from the source through an intermediate comiection." The various amounts of current supplied by these two agencies may be varied by moving the point of connectionbetween each of them In order to avoid opening the currentsupply circuit of a motor when changing the speed therefor, it is customary to make connection to the higher-voltage point before connection is broken with thelow-voltage point, the two points of connection being connected, for the time being, through a preventivedevice embodying either resistance or reactance in order to preventshort circuiting of a portion of the source. By my invention I employ preventive devices of the reactive type and allow them to remain in circuit when connection is made to such portions of the source as are employed for armature supply at high running speeds.

When a motor of the type specified is operating at low speeds, the power factor of the armature circuit is low so that there is a component of the armature current opposed to the current induced in the short circuited armature windings by the cross field winding during the process of commutation. As the speed of the motor is increased, the power factor of the armature circuit improves and theineutralization ceases'to exist, in consequence of whichserious commutator sparking may ensue. By leaving a preventive dev1ce of the reactive type in series with the armature when the latter is running at high speed, the power factor of the armature circult may be lowered to any desired extent in order to insure the neutralization of the above noted reactance commutating voltage under all conditions.

Figure 1 of the accompanying drawing is a diagrammatic view of an alternating-current motor of the series commutating type, together with its attendant control circuits, embodying my invention; and Figs. 2, 3 and 4: are vector diagrams illustrating the operation of the system of Fig. 1.

A11 armature 1 is provided with a main field winding 2 and with a cross field windmg 3, energized from any suitable source of alternating current such, for example, as a transformer 4. The secondary winding of the transformer t is provided with any desired number of voltage taps, such, for example, as 5, 6, 7, and 8. I prefer to provide the cross field winding 3 with more turns than the armature 1 s0 that the current flowing in the armature 1 will be greater than that flowing in the cross field winding 3. At starting, a switch 9 is closed so that the two field windings 2 and 3 are connected in series relation with each other and with the armature winding 1. A connection is made from the armature 1, through the tap 6, to a point in the source of such potential that current will flow therefrom to the armature. The armature current divides at the junction point 12, a portion of it flowing through the windings 2 and 3 and another portion thereof flowing through the taps 6 and a portion of the source. If desired, I may provide the cross field winding 3 with fewer turns than the armature l, whereupon the current flow through the field windings will be greater than that through the armature, and the field current will divide at the point 12, a portion thereof flowing to the source through the tap 6 and the remainder flowing through the armature winding.

VViththe above connections made as noted, the armature 1 will rotate at low speed and the coils thereof that are short circuited by the brushes 13 will have induced therein a rotational electromotive force by the field of the winding 3. At low speed, however,

the power factor of the motor is necessarily somewhat low, and there will be a'component of the armature voltage which is opposed to .the electromotive force induced.

in the short circuited coils. There. will ac cordingly be a neutralization of current in these coils of such magnitude that little. ficulty will be experienced from sparking.

V Tnorder to increase the speed ofthe arma-. ture '1', it is desirable to increase the current flow therethrough though I prefer to accomplish this result by increasing the voltage impressed upon the armature circuit. I, accordingly, close a switch 10 so that connection isfmade .between the taps 6 and 7 through a reactive. devicesll which prevents the short .circuiting of :the portion .of the source included between thetaps 6 .and 17. TheswitchQ is .next opened, whereupon the point 12 is connected to the. tap 7 through the .reactancedevice 11 which is left-in circuit, andthe voltageappliedto thearmature is increased ;from its .former value. The armature ,=then' tends to rotate .at higher speedand also tends to improve .its power factor. As a .result, there-iwould. cease stO be a neutralization. of the .reactance commutating voltage and serious sparking at the brushes wouldensue. By leaving ,the reactance-device 11 .in circuit, however, the power factor of-the armature circuit; may be maintained to such alow value that there will be a-suitable component ofthe armature voltage to opposethe reactance commutating voltage and ,preventsparking.

Theattached Eig. 2 is.a vector diagram for a doubly-fed motor-running at. relatively low. speeds and without an inductance: in the middle tap. I represents the. armature current; I represents they cross field current reduced to,.the armature circuit; Imeross, the cross field ,magnetizingcurrent also reduced tothearmature circuit. E is the inductive voltageon the field which is at right angles-to I E is the voltage impressed upon thecross field circuit; E is the voltage impressed uponthe armature circuit. Ew is ;the voltage which is I induced by transformer action from the cross. field circuit into the armature. Assuminga transformer ratio of 1 to 2, half of thisvoltage :E appearsin the armature and .produces, with i the voltage -,E:.,,

the. r flective-armature VQ1tagelEgi ff-. This voltage is at right angles to the field voltage E and parallel to the. crossfield current which excites .the .main jfield. V The vector c at right angles. to 1 represents the transformer, sparkingvoltage; represents ithe reactance voltage which is in phase with the armature current. These twoQ-sparking voltages combine to produce a voltage e which .is counterbalanced by. .a voltage induced in the .short-circuited coilbyrotation in the cross f eld represented by thevector c By combining said voltage with the other commutation voltvthe armature winding.

ages, .we obtain a as the resultant sparln'ng voltage. In thisparticularcase, thisvoltage is very small and will not cause. any un due arcing, because the reactance sparking voltage .is rather low on account of the low speed. The drops due to ohmic resistance, etc., are neglected as they do not radically modify the diagram and serve only to confuse the showing.

Fig. 3 shows a diagram which is in principle the same as-that of .Fig. 2 exceptithat the'voltage E has been decreased :andnaE increased in order to providean increase .of motor speed. At the same time, -the..re-. actance voltage 0, has 'beenincre'ased :m-a= terially on account of the greater speed. As aresult, the sparking voltage'r isvery large and produces harmful sparking.

Fig. 4 shows how bythe introductionpf the inductance 11 o 7 Fig.1, at hightspeeds, the resultantsparking voltage. is reduced to zero. I represents-the. .currentyflowing in the inductance, :being the difi'erencebe tween the armature .currentand thecurrent Icross flowing in thecross field circuit. The

vector Em representsthe voltage .in the in:

ductance at right anglesto therurrent .in the. same. It will ibe .noted that ..-the..vectors e and e .are .equal and,oppositeto each :other and that, therefore, the motor is fully neutralized for commutation.

Thus, with the very simple controlarrangement shown in Fig. 1, comprising; Q1113 two switches and .an .inductive ,device, it, is

manner.

. Obviously, my invention-is capableofextension overa wide range of speedcontrol, asthe voltageof the armature -mayibe increased by the .use ,of severalmlistinct taps,

with each .of' which is associated a suitable reactance preventive deViGa: the essential condition being that the higherthe voltage applied .to the armature,,with; a, giyen -main and. cross field; strength, the greater a is. the mo nt of eactance nser edinseriss with My system of preventing sparking-and short circuiting ,of the souree may f desired, be combined with ,other .methods of the strength of the. fields 3, biit l do merely g gat ns f distin aprineinlee. Many modificationsof-myinvention will occur to those skilled in. the llaee .cord ngly do not desire .to--be ,restr' h spec c mbod -men ed se q lbu sire that only suc es iietie Shel i-be speedcontro-l such,-for,exampl e, as varying placed upon my invention as are set forth in the appended claims.

claim as my invention: 1. The combination with an alternatingcurrent motor of the commutating type pro vided with an armature winding and a crossfield Winding, of a source of alternating current, means for connecting said armature and cross-field windings in series-circuit re lation across said source, a connection from a point in said series circuit between'said armature and cross-field windings to a point in said source, a second connection includin a reactance device that may be established between said point in the series circuit and a point of different potential than the firstnamed point in said source, and single switching means for interrupting said firstnamed connection and for simultaneously rendering said last named connection. including said reactive device, effective upon the motor circuit.

Copies of this patent may be obtained for five cents each, by addressing the 2. The combination with an alternatingcurrent motor of the connnutating type pro vided with an armature winding and a crossfield winding, of a source of alternating current, means for connecting said armature and cross-field windings in series-circuit relation across said source, a connection from a point in said series circuit between said armature and cross-field windings to'a point in said source, and switching means for simultaneously changing this connection to another point in the source and for increasing the effective reactance of said connection.

In testimony whereof, I have hereunto subscribed my name this 31st day of Aug.

RUDOLF E. HELLMUND.

Witnesses B. B. Hmns.

"Commissioner of Patents Washington, D. 0." 

